JP60-37455A discloses a continuously variable transmission in which a two-forward speed subtransmission mechanism is provided in series with a belt continuously variable speed change mechanism (to be referred to hereafter as a “variator”), and a gear position of the subtransmission mechanism is changed in accordance with an operating condition of a vehicle. Thus, an achievable speed ratio range is enlarged without increasing the size of the variator.
JP5-79554A discloses a technique employed in this type of continuously variable transmission including a subtransmission mechanism for maintaining an overall speed ratio (to be referred to hereafter as a “through speed ratio”) of the continuously variable transmission at a constant value by performing a coordinated shift to vary the speed ratio of the variator in coordination with gear position change performed on the subtransmission mechanism. By maintaining the through speed ratio at a constant value on either side of the coordinated shift, speed variation in an engine and a torque converter during a shift in the subtransmission mechanism is suppressed, thereby preventing shift shock caused by inertia torque from the engine and torque converter.